1. The Field of the Invention
The present invention relates to methods for manufacturing semiconductor devices. More particularly, the present invention relates to a method of resist stripping for use during fabrication of semiconductor devices.
2. The Relevant Technology
During the processing of semiconductor wafers used in the manufacture of integrated circuits and other semiconductor devices, it is necessary in various processing steps to etch or strip certain areas of the wafer to remove photoresist coatings applied to the wafer, and to otherwise clean the wafer. The removal of photoresist coatings by a stripping process typically leaves a residue of resist material on the wafer that can be difficult to remove in a subsequent cleaning process.
Conventional processes for cleaning semiconductor wafers include contacting the wafer with a liquid solvent of a desired composition such as an organic solvent. The composition may be stirred or otherwise caused to flow across or against the surfaces of the wafers to provide a washing action. Cleaning of the wafer utilizing such liquid solvents is typically done by dipping the wafer in a bath of the liquid solvent.
Resist materials have been typically removed from wafers in the past by utilizing a variety of liquid chemical compounds and mixtures. There are several drawbacks with the use of liquid stripping compositions to remove photoresist materials. These include not being able to remove deep UV baked, implant-hardened or plasma hardened photoresist. In addition, use of liquid stripping compositions can leave behind traces of resist film on the wafer as well as non-dissolved yield limiting contaminants originating from the liquid stripping compositions on the wafer.
A resist stripping method utilizing vaporized stripping compositions is disclosed in U.S. Pat. No. 4,867,799 to Grebinski. The method includes positioning a wafer within a treating chamber with the surface to be treated exposed. Ammonia vapor is contacted with water vapor and/or hydrogen peroxide vapor adjacent to the surface of the wafer to provide a hot mixture comprising at least ammonia and ammonium hydroxide which is impinged on the surface of the wafer. The contacting of the ammonia with water and/or hydrogen peroxide is immediately prior to and/or simultaneous with the impinging step.
Other conventional resist strip technologies typically use large amounts of oxygen (O2) to perform the stripping step. The addition of water to O2 to passivate and strip metal etched wafers has also been widely used in the industry.
Other methods of stripping resist coatings utilize O2 plasmas, or combinations of a plasma step and then a liquid acid dip. For example, a microwave stripper system utilizes microwave induced plasma of atomic oxygen at low pressure to strip photoresist from a wafer. Other components such as water and nitrogen can also be used in the microwave stripper system, in either a single step with oxygen, or in a two-step process including passivation and stripping.
Since resist materials are typically made of hydrocarbon polymers, the oxygen utilized in the above resist stripping techniques reacts with carbon in the polymers to form strong carbon-oxygen bonds. Although the oxygen etches the resist very fast, a residue is left having carbon-oxygen bonds, which is difficult to remove in a subsequent cleaning process. The resist is also dehydrated by reaction with the oxygen, which further hardens the remaining residue.
Accordingly, there is a need for improved methods that overcome or avoid the above problems and difficulties.
The present invention is directed to a method of resist stripping for use during fabrication of semiconductor devices. A semiconductor substrate with a resist material formed thereon, such as a silicon wafer, is positioned in a sealed chamber at low pressure in communication with a plasma generating source. A gaseous material that includes a reducing agent such as ammonia is passed through the plasma generating source to produce a plasma stream. The plasma stream is directed at the semiconductor substrate for a predetermined period of time to substantially remove the resist material from the semiconductor substrate. A reducing environment is produced in the sealed chamber by the plasma stream, which can passivate and strip the resist material simultaneously. A conventional wafer cleaning operation can then be easily employed to remove any remaining residue of resist material on the substrate.
The plasma stream utilized in the present invention contains reactive species of ions and radicals that are produced from the gas components of the gaseous material used in forming the plasma stream. The gaseous material used to produce the plasma stream can include various combinations of gas components such as ammonia, water, oxygen, and other optional components
Optionally, the method of the invention can be used in conjunction with another processing step which utilizes a different gaseous material that includes an oxidizing agent to produce another plasma stream. Accordingly, a first gaseous material including a reducing agent is passed through the plasma generating source to produce a first plasma stream, which is directed at the semiconductor substrate for a predetermined period of time to remove a desired amount of resist material. A second gaseous material including an oxidizing agent is passed through the plasma generating source to produce a second plasma stream, which is directed at the semiconductor substrate. The second plasma stream produces an oxidizing environment in the sealed chamber and more quickly strips the resist material.
Other aspects and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.